1. Field
The present disclosure relates to methods and compositions for culturing bacteria. More specifically, the disclosure relates to methods for culturing lactic acid producing microorganisms and formulations for using such microorganisms in the inhibition of pathogenic growth.
2. Description of the Related Art
Beneficial bacteria colonize the intestinal tracts of mammals and can promote the well being of the host. The consumption of exogenous bacteria, often referred to as probiotics, can elicit beneficial effects upon a host. In humans, these probiotic bacteria have been shown to reduce the severity and duration of rotaviral-induced diarrhea, alleviate lactose intolerance, and enhance gastrointestinal immune function (Roberfroid 2000).
Traditionally, food sources such as yogurt have been considered probiotic-carriers providing these health-promoting benefits. It is believed that the consumption of foods rich in probiotic bacteria, including lactic acid bacteria and bifidobacteria, leads to colonization of the human gastrointestinal tract of humans (Roberfroid 2000). The addition of probiotic microorganisms to animal feed can improve animal efficiency and health. Specific examples include increased weight gain-to-feed intake ratio (feed efficiency), improved average daily weight gain, improved milk yield, and improved milk composition by dairy cows as described by U.S. Pat. Nos. 5,529,793 and 5,534,271 issued to Garner and Ware. The administration of probiotic organisms can also reduce the incidence of pathogenic organisms in cattle, as reported by U.S. Pat. No. 7,063,836 issued to Garner and Ware.
Researchers have demonstrated that the consumption of probiotics by animals used in food production can improve the efficiency of animal production. Propionic acid is important in ruminal and intestinal fermentations and is a precursor to blood glucose synthesis (Baldwin 1983). Several examples are available that demonstrate the positive impact of feeding propionic acid-producing organisms to cattle. For example, U.S. Pat. Nos. 5,529,793 and 5,534,271, issued to Garner and Ware, along with U.S. Pat. Nos. 6,455,063 and 6,887,489, issued to Rehberger et al., teach of the beneficial effects that propionic acid-producing bacteria have upon cattle growth. Lactic acid bacteria (LAB) can inhibit pathogens in various food sources. Brashears et al., 2003. Lactic acid producing and lactate utilizing bacteria may also be helpful in inhibiting pathogenic growth in animals and improving the production of dairy products. U.S. Pat. No. 7,063,836. Lactic acid producing and lactate utilizing bacteria are beneficial for the utilization of feedstuffs by ruminants (U.S. Pat. Nos. 5,529,793 and 5,534,271) and have been fed to cattle to improve animal performance. Brashears et al., 2003.
Lactobacillus is the most prevalently administered probiotic bacteria. Flint and Angert 2005. Lactobacillus is a genus of more than 25 species of gram-positive, catalase-negative, non-sporulating, rod-shaped organisms. Heilig et al., 2002. Lactobacillus ferment carbohydrates to form lactic acid. U.S. Pat. No. 7,323,166. They are generally anaerobic, non-motile, and do not reduce nitrate. U.S. Pat. No. 7,323,166. Lactobacillus are often used in the manufacture of food products including dairy products and other fermented foods. Heilig et al., 2002; U.S. Pat. No. 7,323,166. These organisms inhabit various locations including the gastrointestinal tracts of animals and intact and rotting plant material. Heilig et al., 2002; U.S. Pat. No. 7,323,166. Lactobacillus strains appear to be present in the gastrointestinal tract of approximately 70% of humans that consume a Western-like diet. Heilig et al., 2002. The number of Lactobacillus cells in neonates is approximately 105 colony forming units (CFU) per gram CFU/g of feces. Heilig et al., 2002. The amount in infants of one month and older is higher, ranging from 106 to 108 CFU/g of feces. Heilig et al., 2002.
For use as a probiotic, a LAB needs to be able remain viable during processing and storage protocols such as centrifugation, filtration, fermentation, freeze drying or lyophilization in which the LAB may be subjected to freezing, high pressure, and high temperature. U.S. Pat. No. 7,323,166.
Various factors affect the viability of bacteria. Cells are preferably harvested while actively growing in either the logarithmic or early stationary phase with a density of about 108/ml. U.S. Pat. No. 7,323,166. The preservation medium should contain a cryoprotectant such as skim milk, sucrose, serum, inositol, or dextran. U.S. Pat. No. 7,323,166. The preferred cryoprotectant may vary based on the cells to be lyophilized. U.S. Pat. No. 7,323,166.
Probiotics may work by competitive exclusion in which live microbial cultures act antagonistically on specific organisms to cause a decrease in the numbers of that organism. U.S. Pat. No. 7,323,166. Mechanisms of competitive exclusion include production of antibacterial agents (bacteriocins) and metabolites (organic acids and hydrogen peroxide), competition for nutrients, and competition for adhesion sites on the gut epithelial surface. U.S. Pat. No. 7,323,166.
Any substance that is intentionally added to food is considered a food additive and must reviewed and approved by the FDA unless the substance is generally recognized as be in safe. The use of a food substance may be GRAS either through scientific procedures or through experience based on common use in food if the substance was used in food before 1958. (The Federal Food, Drug, and Cosmetic Act (the Act) sections 201(s) and 409 and the FDA's implementing regulations in 21 CFR 170.3 and 21 CFR 170.30; see www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/default.htm.).
The FDA Office of Premarket Approval lists microorganisms that are Generally Recognized as Safe (GRAS) as food additives. Food additives derived from microorganisms that are classified as Generally Recognized as Safe are listed in 21 CFR 170. The FDA has stated that it has no questions regarding the conclusion that a LAB mixture consisting of L. acidophilus (NP35, NP51), L. lactis (NP7), and P. acidilactici (NP3), is GRAS under the intended conditions of use. www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/GRASListings/ucm154589.htm and www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/GRASListings/ucm154102.htm.
Growing conditions for Lactobacillus acidophilus are included in the Jun. 6, 2005 GRAS Notification by Nutrition Physiology Corporation. Jun. 6, 2005 GRAS Notification by Nutrition Physiology Corporation available at www.accessdata.fda.gov/scripts/fcn/gras_notices/grn_171.pdf. Bacteria, including M35, were cultured in NPC-1 media at a temperature range between 35° C. and 42° C. Glucose and lactate were added depending upon the organism. The bacteria were cultured until late stationary phase. The bacteria were concentrated by filtration through a 0.2 micrometer filter system and freeze dried. The freeze dried product was ground into a homogenous powder and stored at −80° C. The powder was mixed with a carrier, the viable cell count determined, and the product was packaged for shipment.
Various strains of LAB were isolated from healthy cattle by plating fecal material on LBS agar and MRS agar plates and placing isolated colonies in MRS broth repeatedly. U.S. Pat. No. 7,323,166.
The application of microorganisms to feed-stuffs is gaining world-wide popularity. Certain direct-fed microbials (DFM) mode of action require cells to be viable to be beneficial to a host. Many DFM products available rapidly lose viable cells and often contain insufficient viable cell concentrations to elicit a positive impact upon the host. Thus, there is need for more efficient methods to produce bacteria that are able to retain a high level of viability and stability during the fermentation and preservation processes.
Corcoran et al. found that Lactobacillus rhamnosus had a greater level of survivability after freeze-drying when the cells were harvested in stationary phase. Cells harvested during log phase demonstrated a 14% survival, while cells harvested in stationary phase showed a 50% survival rate. Correspondingly, the stability of the freeze-dried organisms was also dependent upon the stage of growth harvested. Cells harvested during log phase showed lower levels of stability at incubation temperatures of 4° C., 15° C., and 37° C. than cells harvested during lag or stationary phases.
Mary et al., 1986, found similar results to Corcoran et al., 2004, when evaluating Rhizobium meliloti. Cells harvested during stationary phase showed greater levels of survivability than cells harvested from early-, mid-, or late-log phases.
Fu and Etzel, 1995, evaluated the survival of Lactococcus lactis using different parameters during spray drying of the culture. They reported harvesting the cells in early-stationary phase but did not comment on why they chose that time point or whether they had previously evaluated different times in the growth to harvest the cells.
Teixeira et al., 1995, state that Lactobacillus harvested during log phase are more sensitive to treatments such as spray drying. They demonstrated that Lactobacillus bulgaricus cells harvested during stationary phase had greater levels of survival during spray drying than cells harvested during log growth.
Linders et al., 1998, evaluated the influence of growth and drying conditions upon production of dried Lactobacillus plantarum. They described harvesting the cells 4 hours into stationary phase which resulted in cells with a higher drying tolerance than cells harvested during the log phase of growth.
With regards to stability of different sized cells during preservation, Bozoglu et al., 1987, reported that smaller cells that are closer to spherical in shape, like Streptococcus, are more resistant to freeze-drying than longer, rod shape cells like Lactobacillus. 
Champagne and Gardner reported that the concentration of the fermentable carbon source affected viability of lyophilized Leuconostoc mesenteroides. Cells were grown in either 110 mM (19.8 g/L) or 220 mM (39.6 g/L) glucose in MRS. Cells grown in 110 mM glucose reached 3.6×109 cells/ml while cells grown with 220 mM glucose reached 7.0×109 cells/ml. Although the cells grown with 220 mM glucose achieved greater cells yields, the resulting freeze-dried cultures contained 4.7×1010 cfu/g for cells grown in 110 mM glucose and 3.6×1010 cfu/g for cells grown with 220 mM glucose.
Production of microorganisms is a costly process. Modifications in production that increase cellular yield and retain cell viability can have a dramatic impact upon the profitability of DFM administration. Therefore, further advancement in fermentation technologies are actively sought and needed to maintain a high level of product stability, consumer confidence, and increased profitability for the direct fed microbial industry.